Aluminum-carbon fiber composites

ABSTRACT

1,185,349. Composite metal articles. UNION CARBIDE CORP. 8 Nov., 1967 [21 Feb., 1967], No. 50695/67. Heading B3F. [Also in Division C7] A composite metal article is made by providing a tantalum covering 3 to carbon fibres 2 and filling the voids between the fibres with an aluminium matrix 4. The tantalum covering 3 facilitates the wetting of the fibres by the molten metal. The article is produced by placing the fibres 2 in a cylinder having a number of holes in its sides, heating them in a partial vacuum, submerging the fibres and cylinder in molten aluminium whilst in the partial vacuum and then pressurizing the molten metal to force it into the voids. The fibres may be in yarn or mono-filament form or in fabric or textile form and the carbon may be in a graphitic or non- graphitic form. The tantalum is formed on the carbon fibres by electro-deposition from a fused salt bath, thermal decomposition of the appropriate metal halide, or by sputtering.

6L 9 R. v. SARA 3,473,900

ALUMINUM-CARBON FIBER COMPOSITES Filed Feb. 21, 1967 INVENTOR RAYMOND V.SARA ATTORNEY 3 473 900 ALrJMmrJrvr-cAneoNrrnnn coMrosrrEs Raymond V.Sara, North Olmsted, Ohio, assignor to Union Carbide Corporation, acorporation of New York Filed Feb. 21, 1967, Ser. No. 617,662 Int. Cl.B23 11/00; B2111 39/00 US. Cl. 29195 8 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF INVENTION Field of the invention The present inventionrelates to a composite refractory article which is made up of aplurality of high modulus, high strength carbon fibers which arecompletely coated with a thin layer of tantalum and bonded together byan aluminum matrix.

Description of the prior art Recently, in the space and missileindustries, there has developed a need for materials of constructionwhich exhibit exceptional physical properties, for example, low densitycoupled with high strength and stiffness. Attempts to produce suchmaterials have centered around the fabrication of composite articles.

One of the most promising materials available today for use in compositeform is carbon textiles since they are available commercially in allknown textile forms. Today, it is well known to form composites ofcarbon textiles and resins.

Recently, efiforts have been directed to forming composites of carbontextiles and metals. The object of forming such composites is toincrease the strength of the metal matrix by the inclusion therein ofthe high strength carbon fibers.

Aluminum has been suggested as the matrix media for carbon fiber-metalcomposites which are intended for use in aerospace applications, in themain, due to its low density. However, aluminum does not wet puregraphite for all practical purposes unless aluminum carbide is formed atthe interface. Such an aluminum carbide phase cannot be tolerated due toits thermochemical instability.

In order to overcome the inherent lack of wettability of carbon fiberswith aluminum, it was decided to try and coat carbon fibers with a thinmetallic coating which then would be wetted by aluminum. However, mostmetals react extensively with aluminum above its melting temperature andform one or more brittle intermetallic phases. The intermetallicconstituents or phases either degrade certain mechanical properties ofthe composite or result in dewetting of the aluminum from around thecoated fibers. An extensive study was made of the interfacial zoneformed between titanium, chromium, nickel, copper, columbium, silver,molybdenum, tungsten and tantalum respectively, and aluminum todetermine which metals are most compatible with aluminum and thereforemost useful as intermediate phase-free coupling or wetting agents. Ofall the metals tried only tantalum was found to be entirelysatisfactory.

hired States Patent M 3,473,900 Patented Oct. 21, 1969 SUMMARY Broadlystated, the carbon fiber-aluminum composite article of the inventioncomprises a plurality of carbon iibers each of which is coated with athin layer ofi tantalum and bonded together, preferably in aside-by-side or parallel manner, with an aluminum binder or matrix.Generally, this composite article may be provided by a process whichcomprises coating carbon fibers with a thin but continuous film oftantalum, compacting the socalled fibers into the desired form,infiltrating the voids between the compacted fibers with molten aluminumand cooling the resultant aluminum infiltrated tantalum coated carbonfibers to produce a composite article. This article can then be formedinto any desired shape by known techniques which will readily suggestthemselves to those skilled in the art.

DESCRIPTION OF THE DRAWING The sole figure shown in the drawingpresented herewith is a diagrammatical illustration of a rectangularcarbon fiber-metal matrix composite article produced according to theteachings of the instant invention.

Referring now in detail to the drawing, there is shown in cross sectiona rectangular composite article 1 consisting of aligned graphite fibers2 having disposed on their surface a continuous one to two micron thickcoating of tantalum 3. These so-coated fibers are bonded together by analuminum matrix 4. The graphite fibers 2 are approximately two inches inlength and disposed in the aluminum matrix 4 in a parallel orside-by-side manner. The length dimension of the fibers 2 isperpendicular to surface of the drawing.

DESCRIPTION OF THE PREFERRED EMBODI- MENT OF THE INVENTION Carbontextiles in any form can be employed in the practice of the instantinvention. However, it is preferred to employ carbon fibers in yarn ormono-filament form. Carbon textiles are available commercially and aregenerally produced by the techniques described in U.S. Patents 3,107,152and 3,116,975, among others.

Tantalum can be deposited on the carbon fibers by a variety of methods.The techniques available for accomplishing this includeelectrodeposition from a fused salt bath, thermal decomposition of theappropriate metal halide or sputtering. The exact deposition techniqueto be employed is dictated by a number of factors. Sputtering can beused on relatively complex shapes and results in a tenacious bondbetween the thin tantalum coating and the carbon fiber substrate. Such abond is a highly desirable feature in carbon fiber-metal matrixcomposites. Thermal decomposition of the appropriate halide requires aheating of the carbon fiber substrate and, accordingly, somewhat limitsthe type of shapes which can be coated with tantalum in this manner.Electrodeposition of tantalum from a fused salt bath is an ideal way ofcoating carbon fibers with a thin film of tantalum but this technique islimited to rather simple carbon fiber configurations.

The following example illustrates in detail the preferred practice ofthe instant invention.

A carbon yarn material which had been heated to graphitizingtemperatures was cut into 2 inch lengths. A tantalum coating averagingfrom 0.2 to 2.0 microns was electrodeposited on these fibers by atechnique similar to that described in co-pending US. patent applicationSer. No. 609,683 which has been assigned to the same assignee as theinstant application. These tantalum clad fibers were then placed in analigned position (all parallel) in a cylindrical capillary tube whichwas provided with a top and bottom closure. The surface of the cylinderwas provided with randomly placed holes or openings to facilitate theingress of aluminum into the cylinder and hence into the voids betweenthe aligned carbon fibers. The cylinder containing the carbon fibers ina preselected form was placed into an air tight chamber which alsocontained a vessel of aluminum. The. chamber was then evacuated to apressure of approximately 2X10" mm. of mercury to out gas the carbonfibers. The aluminum was heated to a temperature of approximately 700 C.The cylinder containing the aligned fibers was submerged below thesurface of the molten aluminum. The chamber was then filled with argongas to a pressure of about one atmosphere to insure that molten aluminumfilled essentially all the voids between the aligned carbon fibers.After about thirty seconds of pressurizing the specimen, the capsule waswithdrawn from the molten aluminum, cooled and removed from the chamber.

A metallographic examination of the resultant composite showed thataluminum readily wet the tantalum clad fibers and incorporated them intothe matrix without disturbing the tantalum coating and, moreimportantly, without the formation of a reaction zone at thealuminum-tantalum interface.

Composite so-produced are extremely useful as materials of constructionfor subsonic and supersonic aricraft, space system components andvarious propulsion devices.

While the foregoing example concerns a composite where the fibers arepositioned in a side-by-side relationship, it is readily apparent tothose skilled in the art that the carbon fibers may be randomlyorientated in the aluminum matrix if more isotropic physical propertiesare desired without losing the benefits of the instant invention. Inaddition, it is obvious that the thickness of the tantalum can be variedas desired. All that is required is that it be thick enough to preventthe aluminum matrix metal from coming into contact with the reinforcingcarbon fibers. Likewise, it will be appreciated by those versed in theart that although graphite fibers and fabrics are preferred in thepractice of the instant invention, nongraphitic carbon fibers andfabrics may also be employed. Also, other methods of infiltrating thetantalum clad carbon fibers with aluminum will readily suggestthemselves to the skilled artisan.

The term carbon as used herein and in the appended claims is meant toinclude both the non-graphitic and graphitic forms of carbon.

The foregoing example is presented for illustrative purposes only and isnot intended to unduly limit the reasonable scope of the instantinvention. The limitations or applicants invention are defined by thefollowing claims.

What is claimed is:

1. A refractory composite article comprising a plurality of carbonfibers bonded together by an essentially aluminum matrix, said carbonfibers having a continuous coating consisting essentially of tantalum ontheir outer surface so as to prevent said aluminum matrix from being indirect contact with said carbon fibers.

2. The composite refractory article of claim 1 wherein said fibers aregraphite.

3. The composite refractory article of claim 1 wherein said carbonfibers are in yarn form.

4. The refractory composite article of claim 1 wherein said carbonfibers are arranged in a side-by-side, parallel relationship.

5. The refractroy composite of claim 1 wherein said essentially tantalumcoating on said carbon fibers is in the range of from about 0.2 to about2.0 microns thick.

6. The composite refractory article of claim 2 wherein said graphitefibers are in yarn form.

7. The refractory composite article of claim 2 wherein said graphitefibers are arranged in a side-by-side, parallel relationship.

8. The refractory composite of claim 2 wherein said essentially tantalumcoating on said graphite fibers is in the range of from about 0.2 toabout 2.0 microns thick.

References Cited UNITED STATES PATENTS 2,683,671 7/1954 Findlay et al29l95 X 2,699,415 1/1955 Nachtman 29-195 K 2,920,385 l/l960 Fike et al.29-195 X 3,098,723 7/1963 Micks 29-l83.5 3,085,317 4/1963 Stackhouse29-l94 X 3,384,463 5/1968 Olstowski et al. 29191 X L. DEWAYNE RUTLEDGE,Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 29197, 198

